Acidic deposition process

ABSTRACT

A metallic article is coated with an adherent polymer film by contacting the metallic article with an aqueous bath containing an anionic surfactant stabilized emulsion of a synthetic resinous film forming composition and an oxidizing acid. Interaction of the oxidizing acid and the metallic article produces ions at the surface of the article which ions in turn cause coagulation of the emulsion polymer at the bath-article interface and, thereby, the formation of a coating of the polymer on the surface of the article.

Umted States Patent 1191 1111 3,709,743 Dalton et al. [451 Jan. 9, 1973 [541 ACIDIC DEPOSITION PROCESS 3,185,596 5/1965 Schiffman ..l48/6.16 v 3,053,692 9/1962 1 3,021,228 2/1962 3,519,542 7/1970 Kitamura et al ..14s/5.14 x

Assignee: Celanese Coatings Company, New

York,N.Y.

[22] Filed: June 16, 1971 [2]] Appl. No.: 153,847

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 880,914, Nov. 28,

1969, abandoned.

[52] U.S. Cl. ..148/6.2, 117/113, 117/132 C [51] Int. Cl. ..C23f 7/00, 844d 1/098 [58] Field of Search ..l48/6.2; 117/113, 132 C [56] References Cited UNITED STATES PATENTS 3,585,084 6/1971 Steinbrecher et al ..1 17/132 X 3,592,699 7/1971 Steinbrecher et al ..1 17/132 X 3,397,077 8/1968 Boller et al. ..l48/6.l4 X

Primary Examiner-William D. Martin Assistant Examiner-J-lany J. Gwinnell Attorney-Thomas J. Morgan et a1.

[57] ABSTRACT A metallic article is coated with an adherent polymer I film by contacting the metallic article with an aqueous 11 Claims, No Drawings AClDIC DEPOSITION PROCESS CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of copending application Ser. No. 880,914, filed Nov. 28, 1969, now abandoned.

BACKGROUND OF THE INVENTION The field of art to which this invention pertains is processes for coating metal articles with synthetic resinous film forming compositions.

There are several well known methods of coating metallic articles. In one method the coating is mechanically applied to its substrate, e.g., by roller coating, spraying, brushing, etc. Dip-coating is another method of coating that is commonly used. In this method the article to be coated is dipped into a solution of the coating material. When the article is subsequently withdrawn, a thin film of the coating material remains on the article surface. Yet another coating method is electro-deposition. In this method a coating is applied to a metallic article by dipping it into a solution or dispersion of a coating salt. An electrical charge is then applied to the article and a portion of the coating salt is thereby deposited onto the metallic substrate. An additional coating method is ionic deposition. In this method the substrate to be coated is dipped into a solution of a substance which will coagulate the coating composition. The substrate is then removed and dipped into a second solution of the coating material. In this manner, a film of the coagulated coating material is deposited on the surface of the substrate. In a typical example, a mold is dipped into an ionic solution and then further dipped into a natural rubber latex. A strippable coating of the rubber latex results on the mold.

Each of these methods has several inherent disadvantages. With mechanical coating, oddly shaped articles are very difficult to coat. Often, inaccessible areas are left entirely uncoated or, if they are coated, an uneven thickness of film results. Electrodeposition allows the coating of mechanically inaccessible areas as long as the area is not on a small internal surface. The ability of an electrodeposition resin to coat such internal surfaces is expressed as throwing power. Most, if not all, electrodeposition resins offer less than complete throwing power, especially in very small, deeply recessed interior surfaces.

Dip-coating partially overcomes this problem in that all areas of the substrate exposed to the coating solution are coated. However, this method has several drawbacks. In the first place, the coatings which adhere to the dipped substrate are of the same chemical composition as is the dipping bath itself. Therefore, in their unbaked form, these coatings are quite readily washed off and tend to sag or accumulate on the edges of the coated article. After baking the resulting cured coatings are usually uneven, being much thicker near the edges of the substrate. Finally, using dip-coating, film thickness is difficult to control. Usually such films are thinner than those obtained by other coating methods.

With ionic deposition, thicker films can be obtained than with dip coating, but it is difficult to insure an even distribution of film. This is due, in part, to difficulties in obtaining a uniform coating of the coagulating substance. Usually, since this substance is a salt which must be applied as an aqueous solution, these solutions, having viscosities near that of water, tend to run off the substrate that is to be coated leaving areas where little or no coagulation can occur. Moreover, since ionic deposition is a two step process it is more time consuming than are other simpler coating processes.

SUMMARY OF THE INVENTION This invention relates to a novel process for the coating of metallic articles. Particularly this invention pertains to a process for coating metal articles by contacting the articles with an aqueous emulsion of a synthetic,

resinous, film-forming composition and coagulating a coating of the composition on the surface of the article. More particularly the invention relates to such a process wherein the aqueous emulsion contains an oxidizing acid. This process is referred to as acidic deposition.

An acidic deposition bath can be prepared by dissolving an oxidizing acid, i.e., nitric acid, in a latex, an aqueous emulsion of a synthetic resinous film-forming composition, which is stabilized by an anionic surfactant. The acid used herein, must be able to dissolve a sufiicient amount of the surface of the metallic article which is brought into contact with this bath so as to form metallic ions. These ions must, furthermore, be controlled so that coagulation takes place only at the interface of the bath and the article.

This process offers several advantages over previously described methods of coating. It is superior to normal mechanical application methods in that inaccessible portions of the article to be coated can be covered with an even film. Secondly, it is superior to electrophoretic coating in that all portions of the metallic surface brought into contact with the coating bath are coated. It can be said that acidic deposition resins have essentially percent throwing power.

Acidic deposition is likewise superior to normal dip applications in that coatings can be applied to a greater film thickness and run-off is decreased. Even before baking, acidic deposited films are much more resistant to removal or dissolution by water than are dip-coated films. After baking, acidic deposited films are exceptionally even not having accumulated on the edge of the substrate as is often the case with baked, dip-coated films.

Finally, acidic deposition is superior to ionic deposition in that the article to be coated does not have to be pretreated or impregnated with a coagulating substance. As a result of this, problems in obtaining uniform film thickness are diminished and simplicity of operation is obtained.

DESCRIPTION OF THE INVENTION Acidic deposition as referred to in this invention involves the addition of an oxidizing acid to an aqueous emulsion of a synthetic resinous film forming composition (also called a latex or an aqueous polymeric dispersion) and the subsequent coagulation of this emulsion onto a metal substrate in the form of an adherent coating or film.

Generally, aqueous emulsions of any synthetic, resinous, film forming compositions are satisfactory in forming the acidic deposition baths used herein. ln particular however, the emulsions used should contain polymers or copolymers of vinyl or ethylenically unsaturated polymerizable monomers. Furthermore, it is desirable that these emulsions be prepared in an aqueous medium by addition polymerization in the presence of anionic surfactants. I

The preparation of these emulsions of synthetic film forming compositions can be accomplished by any of the standard emulsion processing techniques. Thus, it is common to charge a portion of the polymerization catalysts or initiators into the reaction flask. The temperature of this mixture is then increased to about 100 F. 200 F. at which time separate additions of the monomers and the remainder of the catalysts are made. Following these additions, the emulsion mixture is held at reaction temperature until substantially complete monomer conversion is attained.

Variations on this procedure include the use of a separate surfactant feed to be carried out during the monomer addition, the use of pre-emulsified monomers, the use of a water-alcohol mixture as the emulsification medium and other well known modifications.

The compositions of the emulsified copolymers can be quite varied. Generally, any of the conventional vinyl or ethylenically unsaturated monomers are useful. For example, the vinyl esters of fatty acids having from one to 18 carbon atoms including vinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinyl oleate, and vinyl stearate can be used. Likewise, the various polymerizable acids such as acrylic, methacrylic, crotonic, itaconic and fumaric acids or maleic anhydride, etc., are useful. Esters of acrylic acid, methacrylic acid, maleic acid, or of other vinyl polymerizable acids with alcohols, glycols or epoxides having from one to 18 carbon atoms can likewise be employed. Examples of such esters include methyl acrylate or methacrylate, ethyl acrylate or methacrylate, propyl acrylate or methacrylate, isopropyl acrylate or methacrylate, the various butyl acrylates or methacrylates, cyclohexyl acrylate or methacrylate, benzyl acrylate or methacrylate, isobornyl acrylate or methacrylate, phenyl acrylate or methacrylate, n-hexyl, n-octyl, 2-ethylhexyl, t-octyl, dodecyl, hexadecyl, or octadecyl acrylates or methacrylates. Acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, styrene, a-methyl styrene, vinyl toluenes, allyl acetate, glycidyl methacrylate, t-butylaminoethyl methacrylate, hydroxyalkyl acrylates or methacrylates, such as hydroxyethyl methacrylate, hydroxypropyl methacrylate or acrylate hydroxyethyl vinyl ether, hydroxyethyl vinyl sulfide, vinyl pyrrolidone, N,N- dimethylaminoethyl methacrylate, ethylene, propylene, vinyl chloride, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, and tetrafluoroethylene can also be used as the monomers herein.

Coatings prepared according to the process of this invention produce films which have excellent wet adhesion. Wet adhesion is defined as the adhesion of the unbaked coating to the particular metallic substrate. Since almost all emulsions are prepared containing water sensitive surfactants, the water resistance of films prepared from these emulsions is a problem. The incorporation of about 15 to 60 solids weight percent of acrylonitrile or methacrylonitrile into the copolymers of the emulsions as prepared herein gives improved water resistance. Water resistance is expressed as percent water up-take. It is determined by immersing a baked coated panel in a bath of boiling water. The heat is then removed and the bath allowed to cool at room temperature for 3 hours. Prior to immersion in the bath, the panel is weighed and the area of its coated surface determined.

Specific film weight total weight of film/total area coated Likewise after the 3 hour immersion period the panel is weighed and the area that was immersed in the bath is determined.

Specific water up-take weight of water absorbed/area of film immersed Using these two determinations the percent water uptake can be calculated.

Percent water up-take specific water up-take/specific film weight It is desirable, but not required, to include, as a component of the copolymers of the emulsions used in this invention, various acid functional polymerizable monomers. Preferred among these monomers are acrylic acid, methacrylic acid, maleic acid and itaconic acid. The incorporation of these acid monomers serves to improve film adhesion to the particular metallic substrate. However, if too large an amount of these acids is used, the water resistance of the resulting films can suffer. Therefore, it is desirable to have from about 0.25 weight percent to about 5.0 weight percent of these acids present based upon the total emulsion solids content.

Finally, in order to prepare films having increased solvent resistance properties, it is desirable to incorporate into the above copolymeric compositions from about 0.25 to about 10 weight percent of a cross-linking monomer. Included are monomers containing epoxide functional groups, e.g., glycidyl methacrylates and acrylates, methylol functional monomers, e.g., methylol acrylamide or methacrylamide and alkylated methylol monomers, e.g., methylated, ethylated or butylated methylol acrylamide or methacrylamide.

Examples of preferred aqueous, emulsified, film forming compositions useful herein include:

1. Homo or copolymers of one to eight carbon alcohol esters of polymerizable acids containing three to four carbon atoms.

2. Copolymers of polymerizable acids containing three to four carbon atoms and one to eight carbon alcohol esters of polymerizable acids containing three to four carbon atoms.

3. Copolymers of polymerizable acids containing three to four carbon atoms, one to eight carbon alcohol esters of polymerizable acids containing three to four carbon atoms and acrylonitrile or methacrylonitrile.

4. Any of the above having, as an additional component, methylol acrylamide or methacrylamide.

5. Any of the above having, as an additional component, isobornyl methacrylate.

6. Any of the above having, as an additional component, a vinyl aromatic monomer, such as styrene or vinyl toluene.

Particularly preferred compositions useful herein are emulsions of copolymers of about 0.5 to 15 weight percent of isobornyl methacrylate, about 0.5 to weight percent of methylol acrylamide or methacrylamide, about to 60 weight percent of acrylonitrile or methacrylonitrile, about 30 to 80 weight percent of a one to eight carbon alcohol ester of a polymerizable acid containing three to four carbon atoms and about 0.25 to 5.0 weight percent of a polymerizable acid containing three to four carbon atoms.

The emulsions useful in this invention are anionically stabilized, i.e., at least 50 weight percent of the stabilizer is an anionic stabilizer, the remainder being a nonionic stabilizer. It is preferred to use all anionic stabilizer. Generally any of the standard anionic stabilizers can be used. These stabilizers (also called emulsifiers or surfactants) are salts generally alkali metal salts of organic acids particularly the sulfates, phosphates or carboxylates. Examples are the sodium salt of alkyloxy polyether sulfate, dioctyl sodium sulfosuccinate, phosphate surfactants in free acid form, sodium lauryl sulfate, sodium dodecyl diphenyl ether disulfate, sodium n-nonyldiphenyl ether disulfate, sodium salt of a polymerized carboxylic acid, sodium salt of polymerized substituted benzoid alkyl sulfonic acid, polymerized potassium salts of alkyl naphthalene sulfonic acids, the sodium, potassium, or ammonium salts of the sulfate esters of alkylphenoxypoly(ethyleneoxy)ethanols, and the like.

Particularly useful in the emulsions of this invention are the co-reactive anionic surfactants which can be used either alone or in combination with nonionic surfactants, anionic surfactants, or both. These co-reactive surfactants can be prepared by forming the alkali metal, amine or ammonia salt of sulfonic, phosphoric or carboxylic acids having sites of polymerizable unsaturation. Examples include the sodium salt of 2-sulfoethyl methacrylate, sodium vinyl sulfonate, the sodium salt of styrene sulfonic acid, as well as the sodium salts of the various polymerizable acids, e.g., acrylic acid, methacrylic acid, itaconic acid, maleic or fumaric acids, or ester acids, etc.

In preparing emulsions from any of the anionic surfactants it is desirable to use the least amount of surfactant that will produce oxidizing acid stable emulsions. Thus, if surfactant levels in excess of six to eight percent based upon the total emulsion monomer content are used, the rate of acidic deposition is greatly slowed. In fact, in some instances, the surfactant level can be increased to such a level that the emulsion will be too stable to coagulate onto a metal article exposed to the acidic bath. On the other hand, the level of surfactant should be sufficient to maintain emulsion stability in the presence of the oxidizing acid.

It can readily be seen that the absolute amount of surfactant required can vary greatly. This amount is controlled by many factors including the monomers, polymer molecular weight, surfactant solubility, and surfactant unit charge. Preferred emulsions can be prepared using the co-reactive surfactants. These surfactants can be used at very low levels (0.5 to 5 percent based on monomers) and still produce oxidizing acid stable emulsions. In particular, the use of these surfactants produces cured films having excellent water and solvent resistance properties.

Furthermore the surfactants that can be used in preparing the emulsions of this invention preferably should not be substantially degraded in the presence of the dilute oxidizing acid systems. For example, sugar (sucrose, dextrose, etc.) or starch based surfactants are in many instances unsatisfactory as emulsion stabilizers for the nitric acid containing acidic deposition baths.

The monomers used herein are polymerized in the usual manner, i.e., by means of a catalytic amount of a conventional free radical polymerization catalyst or catalyst system (which can also be referred to as an addition polymerization catalyst, a vinyl polymerization catalyst or a polymerization initiator). An illustrative but by no means exhaustive enumeration of such catalysts includes inorganic peroxides such as hydrogen peroxide, sodium perchlorate and sodium perborate, inorganic persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, and redox Systems, such as sodium metabisulfite-potassium persulfate, and the like.

In addition other initiators can be used. These include tertiary butyl hydroperoxide, benzoyl peroxide, tertiary butyl perbenzoate, tertiary butyl peroctoate, lauryl peroxide, azo-bisisobutyronitrile (AIBN) and any of the other commonly used initiators.

In order to prepare the acid deposition baths as are used herein, the emulsion which has previously been prepared is placed in a nonmetallic container and the oxidizing acid is added thereto. The solids (polymer content) of the resulting bath can vary from about 2 percent to about the solids level of the emulsion itself, i.e., about percent. However, when controlled film thicknesses and decreased carryout of the bath are desired, it is preferred that the emulsion be diluted with acid and water to a polymer solids content of about 5-20 percent.

The oxidizing acid which is used in the process of this invention is nitric acid which acts upon the particular metallic substrate to be coated, producing a concentration of substrate metal ions at the bath-substrate interface sufficient to cause coagulation of the emulsion onto the metal. The amount of the oxidizing acid that is used herein can vary depending on the stability of the particular emulsion and on the substrate that is to be coated. For example tin plate requires lower acid level baths than does steel. In general the amount of'acid can vary from about 0.1 percent to about 5 percent by weight based upon the total weight of the bath. Preferably this acid content should be in the 0.5 to 2 weight percent range with the pH of the bath being below about 2.

Although the preferred method of incorporating the desired acid system into these baths is to add the diluted emulsion to a solution of the oxidizing acid system, it is also possible to prepare the emulsions in the presence of the dilute acid system itself. This method then eliminates the necessity of post-adding acid to the diluted emulsion.

Generally any iron, zinc, or tin containing metallic substrate can be used in the process of this invention. These metallic substrates will be referred to as ferriferous, zinciferous and stanniferous substrates. Ferriferous is defined to mean iron, steel and other iron alloys wherein iron is the principal constituent, but excluding the so-called stainless steels. Zinciferrous is defined to mean zinc and zinc-alloys wherein zinc is the principal constituent and also galvanized metals, especially hot-dipped and clectrogalvanized iron and steel.

Stanniferous is defined to mean tin and tin-alloys wherein tin is the principal component as well as tin plated metals, particularly tin plated steel. Included are cold rolled steel, phosphatized steel, sand blasted steel, tin free steel, galvanized steel, iron, zinc, tin-plated steel, tin, etc. The only-requirement of the substrate is that it produce sufficient ions to coagulate the particular emulsion on its surface when it is immersed in the oxidizing acid containing bath.

When baths are prepared as above, substrate coating can be carried out at room temperature or lower without difficulty. Likewise the bath temperature can be increased to 50 C. or higher with a corresponding decrease in substrate plating time. In general, plating can be carried out between just above the freezing point of the bath and just below its boiling point, but preferably at about C to about 35 C. The baths, as prepared herein, can be used repeatedly to coat a large number of metal articles. For example, a 10 percent solids emulsion bath placed in a 500 ml.beaker can be used to plate as many as I50 or more 3 inch X 6 inch steel panels. However, if a number of panels are coated sequentially and if no adjustments are made in pH or bath solids, the deposition rate will drop as the number of panels coated increases. It has been found that metal ions, and ammonium ions are accumulated as the time of attack on the metal substrate (corrosion) continues and that nitric acid is rapidly depleted by the corrosion process. Metal ion build-up in the bath has a destabilizing effect and will cause coagulation if sufficiently high concentrations occur. The nitrite ion, an intermediate in the reduction of nitrate to ammonium ion, also can reach significant concentrations in a continuous corrosion of iron. This ion has an inhibiting effect on corrosion and can cause complete cessation of deposition. Finally, depletion of nitric acid from the bath will cause a stoppage of corrosion and of deposition in a continuous process.

The ion content can be controlled by using conventional means for removal of cations and anions, e.g., electrodeposition, precipitation, ion exchange, ultrafiltration, etc. One method for using ion-exchange resin for ion removal is as follows: locate a strong acid cation exchange resin in a container adjacent to the acidic deposition bath; direct a continuous flow of the bath contents into and through the ion exchange resin; route the effluent back into the deposition bath where a continuous or intermittent feeding of the starting emulsion and nitric acid occurs to keep the bath composition constant. When the ion exchange resin approaches the spent stage, the ion removal is taken over by a second ion exchange resin tank, while the resin in the first tank is regenerated by means of a mineral acid.

The process herein disclosed is not limited to the coating of metal panels. Thus, car bodies, sliding material, appliance bodies, metal containers, or any other metallic article can be coated with advantage.

Dipping processes as hereinbefore described are preferred processes. However, any process which provides a means for contacting the metallic substrate with the acid deposition bath is useful in this invention. For instance, a metal tank can be coated by pumping the acidic deposition bath composition into the tank and then removing the bath after a coating of sufficient thickness is obtained. In another variation, the acidic deposition can be applied by roller coating the bath composition onto the substrate. After waiting a short time to allow the emulsion to coagulate, the coating can be washed and dried. Coil coating techniques can also be used wherein the metallic substrate is drawn through a bath and, after coagulation has occurred, the coating is rinsed and baked. Other means of application, such as brushing, spraying, curtain coating, are also useful.

The metal articles are contacted with the bath for a time sufficient to deposit a coating on the article. The contact time will vary depending upon the desired film thickness, the type metal being coated, the composition of the bath, the amount of acid used, etc. Generally such times will vary between about 10 seconds and 30 minutes. The preferred processes are those wherein the time of contact with the bath does not exceed 10 minutes.

Using normal pigmentation techniques, the emulsions of this invention can be formed into paints. The

pigments which are useful, however are preferably limited to those pigments which are non-reactive with the oxidizing acid. For example, barytes, red iron oxide, titanium dioxide, carbon black, magnesium silicate, calcium silicate, etc., are useful. These pigmented emulsions can be employed to coat metallic articles by the processes described herein in the same manner that non-pigmented emulsions can be used.

Following the above deposition step the coated metal articles are preferably rinsed or washed with water and then either air dried or baked using standard methods, i.e., employing temperatures of from F. to 450 F. for a time sufficient to dry and/or cure the coating. In some instances it has been found advantages to carry out a two step baking process. In the first step the substrate is baked at a low temperature (about 85 F. F.) for about 1 minute to 25 minutes. This step allows the removal of water trapped in the coated films. Following this step a higher temperature bake (about 225 F. to 400 F.) is carried out over a like period to insure complete cure of the coating. When cure is used herein it is meant to be synonymous with either crosslinking or drying.

There are two critical requirements for the oxidizing systems used in the acidic deposition process. First, corrosion of the metal substrate and production of cations must proceed at a sustained rate. Second, corrosion must occur without appreciable gassing since gas formation interfers with the adhesion of the coating to the substrate. The corrosion of ferrous substrates by most acids proceeds by means of the reduction of hydrogen ions and consequent evolution of hydrogen gas.

As different mechanism is made possible when the mineral acid contains anionic species which is more electronegative than the hydrogen ion. Some of the possible reactions that occur when iron is placed in dilute nitric acid are as follows:

To substantiate these reactions, the presence of ferrous and ferric ions, NO; and NH, was verified using Atomic Absorption spectrophotometry to detect iron cations, and colorometric methods for the nitrite anions and ammonium cations. The data indicated that accumulation of iron ions and ammonium ions occurs, whereas the concentration of the nitrite ion tends to level off.

In carrying out the process of this invention, the nitric acid in the acidic deposition bath attacks the metal substrate to be coated generating ions. These metal ions in turn act to coagulate the emulsions. Since this coagulation effect occurs at the interface of the metallic article and the emulsion, a film of the emulsion is thereby deposited on the surface of the metallic article.

It is thought that this interfacial coagulation is caused by the metal ions acting to reduce the absolute electrochemical potential or zeta potential of the emulsion particles. Zeta potential is defined as the difference between the movable outer layer emulsion particle charge and the overall charge of the emulsifying liquid. When the magnitude of this charge is reduced sufficiently by a high concentration of metal ions as is found at the emulsion-substrate interface, the individual emulsion particles are then caused to coagulate. This explanation is offered only to clarify the process of the invention herein described. It is not included as a limitation upon this invention.

Coatings obtained by the process of this invention are useful as metal pretreatments, i.e., a thin coating which prevents corrosion of the metal, which can be overcoated with conventional primers and/or topcoats. The coatings can also be used as prime coats over base or pretreated metal, or as one coat systems.

EXAMPLES OF THE INVENTION In the following examples, the surfactants referred to by tradenames are identified as:

Triton QS-44: Rohm & Haas Company anionic phosphate surfactant in free acid form at 80 percent solids in water.

Triton X-lOO: Rohm & Haas Company nonionic octyl phenoxy polyethoxy ethanol at 100 percent solids.

Triton X-200: Rohm & Haas Company anionic sodium salt of alkylaryl polyether sulfonate at 28 percent solids in water.

Daxad 30: Dewey & Almy Chemical Division of W. R. Grace & Co. anionic sodium salt of polymerized carboxylic acid at 25 percent solids in water.

Igepal CO-630: General Aniline & Film Corp. nonionic nonylphenoxypoly(ethyleneoxy) ethanol at 100 percent solids.

Tergitol TMN: Union Carbide Corp. nonionic trimethyl nonyl polyethylene glycol ether at 90% solids in water.

Sipon ES: Alcolac Chemical Corp. anionic sodium salt of lauryl ether sulfate.

Nuodex AF-IOO: Tenneco Chemicals, Inc. an-

tifoaming agent.

Unless otherwise specified all parts and percentages are based upon weight.

EXAMPLE 1 Into a reaction flask equipped with a mechanical agitator, thermometer, nitrogen inlet, reflux condenser and four addition funnels were added 375 grams of water and 12.8 grams of Triton QS-44 surfactant. At 77 F. 100 grams of ethyl acrylate, 100 grams of methyl methacrylate and 4 grams of methacrylic acid were added and agitated for 6 minutes. 4 grams of a solution of 0.3 gram of hydrated ferrous sulfate dissolved in 200 grams of water were then added. A nitrogen flow was begun and the flask contents were cooled to 68 F. with ice. At this point, a solution of 1 gram of ammonium persulfate dissolved in 5 ml. of water, a solution of 0.7 gram of sodium sulfoxylate formaldehyde dissolved in 5 ml. of water and five drops of tertiary butyl hydroperoxide were added. Twenty-five minutes later, a peak exotherm of 147 F. was obtained. The resulting emulsion, when filtered, exhibited a pH of 2.1, a free monomer content of 0.8 percent, and a density of 1.02 grams/ml.

A bath was formed by adding 20 ml. of the above emulsion to a mixture of ml. of water and 10 ml. of a 10% aqueous nitric acid solution. A clean steel panel was placed in this bath and produced a film after 5 minutes immersion. Panels coated in this manner were baked for IS minutes at 262 F. The resulting films were evenly dispersed over all portions of the panels exposed to the bath.

EXAMPLE 2 Into a reactor equipped as described in Example I were added 720 grams of water, 64.8 grams of a 5 weight percent aqueous solution of 2-sulfoethyl methacrylate and 4.8 grams of sodium vinyl sulfonate. To one dropping funnel were added 64.8 grams of a 5 weight percent aqueous solution of the sodium salt of 2-su1fo-ethyl methacrylate, 4.8 grams of sodium vinyl sulfonate, 47.4 grams of a 60 weight percent aqueous solution of N-methylol acrylamide and 120 grams of water. To a second dropping funnel were added 7.8 grams of potassium persulfate, 16.2 grams of itaconic acid and 240 grams of water. To a third dropping funnel were added 28.2 grams of isobornyl methacrylate, 367.8 grams of acrylonitrile and 658.2 grams of butyl acrylate.

The flask contents were heated with stirring to 149 F. under a continuous nitrogen flow. 7.8 grams of sodium metabisulfite were added followed by a separate and concurrent addition from each of the three dropping funnels over a three hour period. When these additions were completed, the reaction temperature was increased to 167 F. and 60 drops of tertiary butyl hydroperoxide were added. After 1.5 hours an additional 60 drops of tertiary butyl hydroperoxide were added. Heating was then continued for 2.5 hours. The resulting emulsion had no free monomer content, a density of 1.02 g./ml., a pH of 2.72 and a Brookfield viscosity at 25 C of 24 cps (No. 1 spindle, 20 rpm).

A bath was prepared by adding 20 ml. of the above emulsion to ml. of water and 5 ml. of a 10 percent aqueous nitric acid solution. After immersing clean cold rolled steel panels in this solution for 5 minutes and baking them for 20 minutes at 350 F., 0.5 to 0.7

mil films which covered all the panels exposed to the bath were produced.

EXAMPLE 3 An emulsion was prepared similar to Example 2 except that the contents of the third dropping funnel were replaced by 699 grams of butyl acrylate and 367.8 grams of acrylonitrile. Solidscontent of the emulsion was 37 percent.

A bath was prepared by adding 20 ml. of the above emulsion to 70 ml. of water and 10 ml. of a percent aqueous nitric acid solution. Panels of both zinc phosphate treated steel panels and cold rolled steel were immersed in this bath for minutes each and baked at 140 F. for 7 minutes followed by 5 minutes at 300 F. Films were also prepared from the emulsion itself on a second set of panels using a 3 mil draw-down blade. The films were air dried and baked at 300 F. for 5 minutes. Both sets of panels were placed in salt spray for 48 hours. The panels coated by the acidic deposition process showed greatly improved corrosion resistance over the conventionally coated panels.

A pigment base was prepared by mixing 6 grams of magnesium silicate, 12 grams of barytes, 12 grams of red iron oxide, 12.8 grams of water, 0.8 gram of Daxad 3O surfactant, 0.8 gram of lgepal CO 630 surfactant and 0.8 gram of Nuodex AF-lOO defoamer. This paste was ground on a Cowles grinder and 10 ml. of it were mixed with ml. of the emulsion prepared above, 65 ml. of water and 5 ml. of a 10 percent aqueous nitric acid solution. Steel panels were immersed in this bath for 5 minutes and baked for 30 minutes at 300 F., producing a continuous, dried pigmented coating.

EXAMPLE 4 Using substantially the same procedure as was described in Example 2, an aqueous emulsion was prepared from 105 grams of butyl acrylate, 61.3 grams of acrylonitrile, 4.7 grams of glycidyl methacrylate, 4.7 grams of isobornyl methacrylate, 2.7 grams of itaconic acid, 7.9 grams of a 60 percent aqueous solution of methylol acrylamide, 21.6 grams of a 5 percent aqueous solution of the sodium salt of 2-sulfoethyl methacrylate, 1.6 grams of sodium vinyl sulfonate, and 180 grams of water, using 1.3 grams of potassium persulfate and 1.3 grams of sodium metabisulfite, followed by 20 drops of tertiary butyl hydroperoxide. The resulting emulsion had a solids content of 47.6 percent (48.1 percent theoretical), a density of 1.03 grams/ml, a pH of 3.0 and a free monomer content of less than 0.1 percent.

A bath was prepared by adding 20 ml. of the above emulsion to 75 ml. of water followed by the addition of 5 ml. of a 10 percent aqueous nitric acid solution. Six cold rolled steel panels. were immersed in the above bath for 5 minutes, washed, baked for 5 minutes at 140 F. and then baked at 300 F. for 5 minutes. Water uptake tests were run on all panels with the up-take percentages varying from 3.04 percent to 3.98 percent.

EXAMPLE 5 Using substantially the same procedure as described in Example 2 an emulsion was prepared similar to that described in Example 4 but with the 4.7 grams isobornyl methacrylate, 4.7 grams glycidyl methacrylate, and 105 grams butyl acrylate being replaced with 18.6 grams of isobornyl methacrylate, and 95.7 grams of butyl acrylate. The emulsion exhibited a pH of 3.30, a density of 1.04 grams/m., a solids content of 47.9 percent and a monomer conversion of 99.5 percent.

A. Two cold rolled steel panels were dipped in a 0.5 percent aqueous solution of nitric acid for 5 minutes, dried, and then dipped in a portion of the above emulsion for 5 additional minutes. These panels were then baked for 5 minutes at 140 F. followed by a 5 minutes bake at 300 F.

B. Two cold rolled steel panels were immersed for 5 minutes in another portion of the above emulsion and baked as above (5 minutes at 140 F. followed by 5 minutes at 300 F.

C. A third pair of cold rolled steel panels were immersed for 5 minutes in a bath prepared by mixing 20 mls of the above emulsion, 10 ml of a 5 percent aqueous nitric acid solution and mls of water. These coated panels were then baked as above.

Using the same bath as in C., 4 additional steel panels were coated in the bath for 5 minutes and then discarded. Following this, two more test panels (cold rolled steel) were immersed in the bath, coated for 5 minutes and then baked as above.

A water up-take was run on all panels with the following results:

Using substantially the same procedure described in Example 2, an aqueous emulsion was made from 1 16.5 grams of butyl acrylate, 61.3 grams of acrylonitrile, 2.7 grams of methacrylic acid, 4.5 grams of a 60 percent aqueous solution of N-methylol acrylamide, 0.54 gram of sodium vinyl sulfonate, 0.54 gram of a 5 percent aqueous solution of the sodium salt of Z-sulfoethyl methacrylate in 202 grams of water using 1.3 grams of potassium persulfate, 1.3 grams of sodium metabisulfite, 0.2 gram of sodium hydroxide and 8 drops of tertiary butyl hydroperoxide. The pH of the resulting emulsion was adjusted to 8.5 with aqueous ammonium hydroxide. The percent solids was then i found to be 47.1.

A bath was prepared by blending 20 ml. of the above emulsion with ml. of water and 5 ml. ofa 10 percent aqueous nitric acid solution. Tin plated steel panels were dipped into this bath for 20 seconds, rinsed with water and baked first at F. for 7 minutes, then at 302 F. for 10 minutes. Panels prepared in this manner were tested for water up-take by immersing them in a container of boiling water. The container and the water were then allowed to cool at room temperature. Three hours after immersion the panels were removed. The weight of the various panels increased by an average of 1.1 percent.

One day later the above acidic deposition bath was still stable and plated out excellent films on zinc phosphate treated steel panels after minutes immersion time.

Two days later the same bath was used to plate films on cold rolled steel panels using a 5 minute deposition time. These steel panels were baked for 7 minutesat 300 F. producing films having an average pencil hardness of 2H-3H.

EXAMPLE 7 Using the same procedure as described in Example 2, an emulsion was made using the same components in the same amounts as were used in Example 6 except 21.6 grams of 2 sulfo-ethyl methacrylate were used in place of the listed surfactants. The emulsion exhibited a solids content of 46.9 percent, a density of 1.03 grams/ml., and a 01 spindle, rpm, C. Brookfield viscosity of 80 cps.

A bath was prepared by adding 20 m1. of the above emulsion to 75 ml. of water and 5 ml. of a 10 percent aqueous nitric acid solution. A cold rolled steel panel was immersed in this bath for 5 minutes and baked for 10 minutes at 250 F. The resulting coating exhibited excellent appearance, a reverse impact of 28 inch-lbs., a pencil hardness of 2H-3l-l, fair mar resistance and good adhesion.

Using the same bath an additional cold rolled steel panel was immersed for 5 minutes and baked for 7 minutes at 140 F. followed by 10 minutes at 300 F. The coating which resulted exhibited a 3.1 percent water up-take.

A tin free steel panel was immersed in the above bath for 5 minutes and baked for 10 minutes at 250 F. The resulting coating exhibited properties similar to those exhibited on the cold rolled steel panel previously evaluated.

A zinc panel was immersed in the above bath for 3 minutes and baked for 10 minutes at 250 F. resulting in a coating having properties equivalent to those obtained on cold rolled steel.

A tin plated steel panel was immersed in the above bath for 20 seconds, baked at 250 F. for 10 minutes and evaluated. 1t exhibited coating properties equivalent to those obtained in the previous examples. Using the same immersion time (20 seconds) but a 7 minute 240 F. bake, followed by a 10 minute 300 F. bake, a tin plated steel panel was evaluated for water up-take. The panel weight increased by 1.1 percent after 3 hours immersion.

A paint base was prepared by mixing 300 parts of titanium dioxide, 128 parts of water, 8.0 parts of Daxad surfactant, 8.0 parts of Triton 100 surfactant, and 4.0 parts of Nuodex AF-lOO defoamer. 44.8 parts of this base were mixed with 63 parts of the emulsion prepared above. Twenty ml. of this mixture were then added to 70 ml. of water and 10 ml. of a 5 percent aqueous nitric acid solution. Panels of tin plated steel and cold rolled steel were both immersed and, when baked, producted pigmented, continuous dried coatings.

EXAMPLE 8 Using the same procedures previously described, an aqueous emulsion was made from the following comonomers: 106.5 grams of butyl acrylate, 71.3 grams of acrylonitrile, 2.7 grams of methacrylic acid and 7.2 grams of a 60% aqueous solution of N-methylol acrylamide. The surfactant used was sodium lauryl sulfate in the amount of 3.6 grams of a 30 percent aqueous solution. The catalysts used were sodium persulfate and sodium metabisulfite in the amount of 1.3 grams each, followed by the addition of 10 drops of tertiary butyl hydroperoxide. The pH of the resulting emulsion was adjusted to 8.5 with aqueous ammonia. The emulsion had a solids content of 47.2 percent (47.6 percent theoretical), a density of 1.04 grams/ml. and a Brookfield viscosity at 25 C. of 60 cps (No. 1 spindle, 20 rpm).

A bath was prepared by adding 20 ml. of the above emulsion to ml. of water and 10 ml. of a 10% aqueous nitric acid solution. Tin plated steel panels were soaked in Cellosolve acetate, dried, placed in the above bath for 5 minutes, removed and baked for 7 minutes at F. This procedure produced a coating having a pencil hardness of 31-1-41-1 and goodadhesion and mar resistance.

EXAMPLE 9 To a reaction flask equipped with a mechanical agitator, thermometer, nitrogen inlet and 4 addition funnels were added 245 grams of water. The water was heated to 108 F. and 16.5 grams of Triton X-200 surfactant were added. After agitating the mixture for 30 minutes, the reaction flask was flushed with nitrogen. Previously, to the first addition funnel had been added 12.35 grams of a 60% aqueous solution of N-methylol acrylamide, 3.60 grams of itaconic acid and 20.65 grams of sodium dodecyl diphenyl ether disulfonate in 64 grams of water. To the second addition funnel had been added 0.7 gram of potassium persulfate in 35 grams of water. To the third addition funnel were added 0.7 gram of sodium metabisulfite in 35 grams of water. To the fourth addition funnel were added 217.5 grams of ethyl acrylate and grams of methyl methacrylate. After flushing the flask with nitrogen for 30 minutes, about 10 percent of the monomer mixture from the fourth addition funnel was added. About A of the contents of the second funnel (the catalyst solution) was then added, followed in 5 minutes by half the contents of the third funnel (the reducing agent solution). 20 grams of water were 'then added to the remaining content of the second addition funnel. The reaction temperature was increased to 140 F., and four separate additions were conducted the contents of the first and fourth funnels were added over 4 hours; the contents of the second and third over 4-% hours. When the additions were completed, the reactants .were held at 140 F. for 15 minutes and 0.2 gram of sodium sulfoxylate formaldehyde in 1.0 gram of water was added along with 0.55 gram of tertiary butyl hydroperoxide. The temperature was held at 149 F. for 30 minutes. After cooling, the pH of the emulsion was adjusted to about 6 with 10 percent aqueous sodiurn hydroxide. This emulsion had a solids content of 47.3 percent (52 percent theoretical) and a spindle No. 3, 10 rpm, Brookfield viscosity of 5600 cps.

A bath was prepared by adding 20 ml. of the above emulsion to 70 ml. of water and 10 m1. of a 10 percent aqueous nitric acid solution. Tin plated steel panels,

prior to use, were cleaned with acetone and dried. A panel was immersed for 12 seconds in the above bath and baked for minutes at 1 13 F. The resulting coating exhibited a pencil hardness of F-H, and good appearance, acetone resistance and adhesion. The emulsion as prepared was drawn down on a tin plated steel panel and baked. The coating obtained in this manner was decidedly poorer in acetone resistance, water resistance, mar resistance and adhesion than was the coating obtained by the acidic deposition process.

Using the same acidic deposition process, 22 additional panels were coated with no significant differences seen between any of the coatings.

EXAMPLE A reaction flask equipped as in Example 9 was charged with 376 gramsof water and 24 grams of Triton X200 surfactant. This mixture was agitated for 10 minutes and 70 grams of methyl methacrylate, 100 grams of butyl acrylate, 25 grams of hydroxy propyl methacrylate, 7 grams of glacial acrylic acid, 20 ml. of a percent aqueous solution of ferrous sulfate and 1 gram of ammonium persulfate dissolved in 5 ml. of water were added. This new reaction mixture was stirred for an additional 10 minutes and then cooled to 68 F. with an ice bath. At this point, seven drops of tertiary butyl hydroperoxide and 0.7 gram of sodium sulfoxylate formaldehyde dissolved in 5 ml. of water were added and the entire reaction mixture was heated to 153F. After about 1-% hours at 153 F., polymerization was completed as evidenced by the reaction mixture having a solids content of 31.9 percent versus'33.9 percent theoretical. The resulting emulsion was filtered through cheesecloth and cooled.

A bath containing ml. of the above polymer 10 ml. of a 10% aqueous nitric acid solution and 70 ml. of water was prepared. A steel panel was immersed therein for 30 minutes, air dried for 30 minutes and baked for 30 minutes at 140 F. A smooth coating having good appearance resulted. Similar baths were prepared based upon hydrochloric and hydrofluoric acids. No coatings were produced. Another similar bath using 5 ml. rather than 10 ml ofa 10 percent aqueous nitric acid solution produced thinner films on steel.

EXAMPLE 1 1 Using a reaction flask equipped with a mechanical agitator, thermometer, addition funnel, nitrogen inlet and a reflux condenser an emulsion was prepared by adding an initial charge of 120 grams of water and 4.0 grams of a 30 percent aqueous solution of sodium lauryl sulfate to the reaction flask. This mixture was then heated to 149 F. with continuous nitrogen flow and agitation, and 1.3 grams of sodium metabisulfite were added. Immediately following this addition, simultaneous 2-%-hour additions were made of: a surfactant feed of 4.0 grams of a 30 percent aqueous solution of sodium lauryl sulfate, 21.5 grams of water, and 4.5 grams of a 60 percent aqueous solution of methylol acrylamide; a catalyst feed of 40 grams of water and 1.3 grams of potassium persulfate; and a monomer feed of 116.5 grams of butyl acrylate, 61.3 grams of acrylonitrile and 2.7 grams of methacrylic acid. At the end of these additions eight drops of tertiary butyl hydroperoxide were added, the reaction mixture was heated to 167 F. and

held for an additional 2- /4 hours. The resulting emulsion exhibited substantially complete monomer conversion with a solids content of 47.9 percent.

A bath was prepared by mixing 20 ml. of the above emulsion, 10 ml. of a 10 percent aqueous nitric acid solution and 70ml. of water. Steel panels immersed therein for five minutes were washed, baked at 140 F. for 5 minutes, post-baked for 5 minutes at 300 F. and evaluated. Good coatings were found to cover all portions of the panels which had been exposed to the bath.

EXAMPLE 12 A reaction flask was equipped with a thermometer, nitrogen sparge inlet, reflux condenser, mechanical agitator and 3 monomer addition tubes with funnels. An initial charge of 120 grams of water, 10.8 grams of a 5 percent aqueous solution of the sodium salt of 2-sulfoethyl methacrylate, and 0.8 grams of sodium vinyl sulfonate were added to the reaction flask and the entire mixture was heated to 149 F. with continuous agitation and nitrogen flow. 1.3 grams of sodium metabisulfite were added when the temperature of the initial charge became stable at 149 F. Simultaneously the addition of: (1.) a surfactant feed comprising 10:8 grams of a 5 percent aqueous solution of the sodium salt of 2-sulfoethyl methacrylate, 0.8 grams of sodium vinyl sulfonate, 21.5 grams of water and 4.5 grams of a 60% aqueous solution methylol acrylamide; (2.) a catalyst feed comprising 40 grams of water, 2.7 grams of itaconic acid and 1.3 grams of potassium persulfate and; (3.) a monomer feed of 1 16.5 grams of butyl acrylate and 61.3 grams of acrylonitrile were begun and each separate addition was carried out over a 2-V2 hour period. At the end of this addition period, eight drops of tertiary butyl hydroperoxide were added and the reaction mixture was heated to 167 F. and held for an additional 2-% hours. The resulting emulsion exhibited substantially complete monomer conversion with a I solids content of 47.9 percent. When cooled this emulsion was neutralized with aqueous ammonia and filtered through cheesecloth.

20 ml. of the emulsion were mixed with ml. of distilled water and 5 ml. of a 10 percent aqueous nitric acid solution. Clean steel panels were immersed in this bath for 5, 10, and 15 minutes respectively. In each instance a film plated onto the immersed panel. All panels were then baked for 3 minutes at F. and post baked at 300 F. for 5 minutes. Each panel exhibited a pencil hardness of from 2H-3H and good appearance.

EXAMPLE 13 Using the same procedure as in Example 12, an emulsion was prepared having the same composition as Example 12 except that the surfactant feed contained, in addition, 0.8 gram of Tergitol TMN surfactant.

An acidic deposition bath was prepared by adding 20 ml. of the above emulsion to a mixture of 70 ml. of water and 10 ml. of a 10 percent aqueous nitric acid solution. Steel panels were immersed in this bath for five minutes, baked for 5 minutes at 140 F. and further baked for 5 minutes at 300 F. Good coating was obtained on all panels.

EXAMPLE 14 An acidic deposition bath was made at 10 percent polymer solids in water using an aqueous emulsion of a copolymer of 59 percent isobutyl acrylate, 33 percent styrene, 2.5 percent isobornyl methacrylate, 2.5 percent N-methylol acrylamide, 1.5 percent itaconic acid, 0.9 percent sodium vinyl sulfonate and 0.6 percent sodium salt of 2-sulfoethy1 methacrylate. The pH of the bath was adjusted with nitric acid and cold rolled steel (CRS) panels, zinc phosphate treated panels (ZPS) and iron phosphate treated panels (IPS) were immersed in the bath for 5 minutes. The coated panels were removed from the bath, allowed to drain for 60 seconds and were rinsed under a stream of tap water. The panels were then baked for 5 minutes at 360 F. Evaluation of these coated panels are listed below:

An acidic deposition bath was made at percent polymer solids in water using an aqueous emulsion of a copolymer of 59.5 percent butyl acrylate, 30 percent styrene, 10 percent acrylonitrile and 0.5 percent maleic acid, stabilized with 1.83 percent (based on monomers) of Sipon ES surfactant. The pH of the bath was adjusted with nitric acid and cold rolled steel panels (CRS), zinc phosphate treated panels (ZPS) and iron phosphate treated panels (IPS) were immersed in the bath for 5 minutes. The coated panels were removed from the bath, allowed to drain for 60 seconds and were rinsed under a stream of tap water. The panels were then baked for 5 minutes at 360 F. Evaluation of the coated panels are listed below.

pH Substrate Wet Film Thickness (mils) Adhesion Polished Unpolished Side Of Side of Panel Panel Fair to 1.1 ZPS Good 1.11 1.19

. ZPS Poor lrregular 1.1 1P5 Good 0.98 0.73 IPS Good 0.68 0.68 1.1 CRS Good 0.12 1.05 2.0 CRS Fair 0.18 0.13

bath which chemically attacks the surface of the metal article and generates ions which render the emulsion unstable adjacent to the surface and cause coagulation of the emulsion on the surface, wherein said bath contains (1 an anionically stabilized aqueous emulsion of a synthetic resinous film-forming composition wherein the resinous film-forming composition is present in the amount of 2-65 percent by weight based on the total weight of the bath, (2) nitric acid in the amount of 0.1 to 5 percent by weight based on the total weight of the bath and (3) water.

2. The process of claim 1 wherein the resinous filmforming composition is present in the amount of 5 to 20% by weight based on the total weight of the bath and the nitric acid is present in the amount of 0.5 2% by weight based on the total weight of the bath.

3. The process of claim 1 wherein the resinous filmforming composition is a homopolymer or copolymer of ethylenically unsaturated polymerizable monomers.

4. The process of claim 1 wherein pigments are added to the bath to produce pigmented coatings.

5. The process of claim 1 wherein the emulsion is stabilized with 50 to weight percent anionic surfac tant and 0 to 50 weight percent nonionic surfactant.

6. The process of claim 1 wherein the synthetic resinous film-forming composition is a homopolymer or copolymer of ethylenically unsaturated polymerizable monomers.

7. The process of claim 6 wherein the copolymer contains 0.25 to 5.0 weight percent based on the copolymer of a polymerizable acid which contains three to four carbon atoms.

8. A process for coating ferriferous, zincferrous and stanniferrous metal articles which comprises:

A. contacting the articles for a time sufficient to form a coating thereon with an aqueous emulsion containing bath which chemically attacks the surface of the metal article and generates ions which render the emulsion unstable adjacent to the surface and cause coagulation of the emulsion onto the surface, wherein said bath contains 1. an anionically stabilized aqueous emulsion of a synthetic resinous film-forming composition wherein the resinous film-forming composition is present in the amount of 2-65 weight percent based on the total weight of the bath,

2. nitric acid in the amount of 0.1 to 5 weight of the bath and 3. water:

B. removing the article from contact with the bath;

C. rinsing the article with water and D. heating the article at about F. to about 450 F. for a time sufficient to dry the coating.

9. The process of claim 8 wherein the resinous filmforming composition is a homopolymer or copolymer of ethylenically unsaturated polymerizable monomers and is present in the amount of 5 to 20 weight percent based on the total weight of the bath and the nitric acid is present in the amount of 0.5 to 2 weight percent based on the total weight of the bath.

10. The process of claim 9 wherein pigments are added to the bath to produce pigmented coatings.

11. The process of claim 9 wherein the emulsion is stabilized with 50 to 100 weight percent anionic surfactant and 0 to 50 weight percent nonionic surfactant. 

2. The process of claim 1 wherein the resinous film-forming composition is present in the amount of 5 to 20% by weight based on the total weight of the bath and the nitric acid is present in the amount of 0.5 - 2% by weight based on the total weight of the bath.
 2. nitric acid in the amount of 0.1 to 5 weight of the bath and
 3. water: B. removing the article from contact with the bath; C. rinsing the article with water and D. heating the article at about 150* F. to about 450* F. for a time sufficient to dry the coating.
 3. The process of claim 1 wherein the resinous film-forming composition is a homopolymer or copolymer of ethylenically unsaturated polymerizable monomers.
 4. The process of claim 1 wherein pigments are added to the bath to produce pigmented coatings.
 5. The process of claim 1 wherein the emulsion is stabilized with 50 to 100 weight percent anionic surfactant and 0 to 50 weight percent nonionic surfactant.
 6. The process of claim 1 wherein the synthetic resinous film-forming composition is a homopolymer or copolymer of ethylenically unsaturated polymerizable monomers.
 7. The process of claim 6 wherein the copolymer contains 0.25 to 5.0 weight percent based on the copolymer of a polymerizable acid which contains three to four carbon atoms.
 8. A process for coating ferriferous, zincferrous and stanniferrous metal articles which comprises: A. contacting the articles for a time sufficient to form a coating thereon with an aqueous emulsion containing bath which chemically attacks the surface of the metal article and generates ions which render the emulsion unstable adjacent to the surface and cause coagulation of the emulsion onto the surface, wherein said bath contains
 9. The process of claim 8 wherein the resinous film-forming composition is a homopolymer or copolymer of ethylenically unsaturated polymerizable monomers and is present in the amount of 5 to 20 weight percent based on the total weight of the bath and the nitric acid is present in the amount of 0.5 to 2 weight percent based on the total weight of the bath.
 10. The process of claim 9 wherein pigments are added to the bath to produce pigmented coatings.
 11. The process of claim 9 wherein the emulsion is stabilized with 50 to 100 weight percent anionic surfactant and 0 to 50 weight percent nonionic surfactant. 